A bomb attack targeting a van carrying Pakistani policemen killed 12 and wounded more than 50 others Thursday in the northwestern city of Karachi.

Officials said many of the wounded are in critical condition.

In an emailed statement, a spokesman for the Pakistani Taliban claimed responsibility for the attack and said it was retaliation for the recent killing of more than 20 insurgents by police and paramilitary rangers.

Police say a car packed with explosives was parked along the police vehicle's route. It detonated when the two vehicles were side by side.

The attack, the latest in a series of violent incidents, comes in the midst of government efforts to meet with Taliban leaders in the hope of ending nearly a decade of insurgency in northwestern Pakistan.

The Taliban has said it will continue such attacks until there is an agreement on a formal ceasefire.

The Karachi attack comes a day after nine people were killed on the outskirts of the city of Peshawar, near the border with Afghanistan. Officials say at least a dozen men surrounded the home of a Pakistani police officer and hurled grenades into the building. The police officer himself was killed in a shootout last Sunday.

On Tuesday in Peshawar, at least 11 people were killed after assailants threw grenades into a crowded movie theater. At least 20 others were wounded.